Anyone who claims they are a "fan" of a particular sports team, even though they had no prior support for/interest in the team until that team started winning. These types of fans only show playoff interest, have probably never watched a regular season game, don't own any type of team merchandise, nor would they buy any.

Everyone in Cleveland became a bandwagon fan only after LeBron James got drafted and they made the playoffs.

Switches support to whatever team/game/allegiance/belief happens to be successful at the time

"Brothers in Arms fans were pissing there pants once they played Call of Duty:World at War, now they're saying the its the most authentic game ever. And all this because the MP of Brothers in arms:Hell's Highway sucked... Such worthless bandwagon fans"

Whenever a region's sports team suddenly gets really good really quickly, everyone and their fucking dog either buys a sports jersey or takes their old one out of the closet where it's been for 20 years, proclaiming they are a diehard fan. Bandwagon fans usually flock to their team's games in large numbers and usually constitute 80% of that team's fanbase. See Florida Gators.

Most common in sports, a bandwagon fan is a fan of a team simply because they are the reigning champions/have the most championships/doing the best at the moment. The second these fans notice that they're team is starting to do poorly, they'll jump ship and hop on the bandwagon of a different team that is doing well. As a result, they will have little to no knowledge of their current team and the true fans of said team will hate them for it.